The manufacture of tires typically involves a tire building drum wherein numerous tire components are applied to the drum in sequence, forming a cylindrical shaped tire carcass. This stage of the tire building process is commonly referred to as the “first stage” of the tire building process. The tire carcass is then typically removed from the tire building drum and sent to a second stage, expandable tire shaping drum where the carcass is expanded into a toroidal shape for receipt of the remaining components of the tire such as the belt package and a rubber tread. The completed toroidally shape unvulcanized tire carcass or green tire is then removed from the second stage drum and subsequently molded and vulcanized into a finished tire.
The prior art process thus requires two tire building drums and the transfer of the carcass from one drum to the other. Further, a problem often arises in precisely locating and anchoring the tire beads on the unvulcanized tire carcass, especially during the transportation of the tire beads from the first stage drum to the second stage drum. Variations in bead positioning can result in ply distortion in the tire.
Tire manufacturers have recently begun moving towards the utilization of a single tire building drum, for both the first and second stage tire building. This requires that the tire building drum be capable of axial expansion and contraction as well as radial expansion/contraction. Further, it is important to maintain a positive bead lock during the entire tire building process, including the tire shaping, so that the ply cord length is maintained, resulting in good tire uniformity.
Tire manufacturers typically use a flexible cylindrical rubberized center sleeve as the outermost element on tire building drums. The center sleeve functions as the surface of application and point of fixation for the innermost component of the tire (innerliner). The section where the centersleeve wraps around the “shoulder” of the radially expansible segments also serves as a pneumatic seal against the bead area of the green tire, enabling inflation (shaping) of the green tire in the full-stage tire building process. The centersleeve also typically has a series of holes for providing a vacuum to secure the innerliner to the drum and the air to shape the green tire.
There are several disadvantages to the prior art rubber center sleeves. The tire building drums typically have a wide range of width adjustability, while the prior art rubber center sleeves have a very limited range of width operation, typically less than 30 mm. Thus the sleeve limits the action of the tire building drum, resulting in the need to change out the drum with another drum having a different width centersleeve in place. The necessity of changing out of the drum requires the storage of drums for different width sizes, and the loss in productivity during the drum change outs.
A second disadvantage to the prior art center sleeves is that during the tire building cycle the drum width is progressively reduced as the shaped diameter of the green tire increases. This reduced width action may result in the bunching up or buckling of the sleeve due to compression. As the buckled diameter is larger than the bead diameter of the tire, it is necessary to widen the width of the tire building drum in order to remove the finished tire from the drum.
A third disadvantage to the prior art center sleeves is that they are the highest maintenance component on the tire building drum, requiring frequent replacement when they become torn or blistered.
A fourth disadvantage to the prior art center sleeves is that the use of the sleeve results in an increased amount of force required to expand the drum.
A fifth disadvantage to the prior art center sleeves is that the use of the sleeve can result in uneven air flow distribution during inflation of the carcass, contributing to tire nonuniformity.